The present invention generally relates to improved photoresist processing. In particular, the present invention relates to reducing electrostatic charges on developed photoresists using an improved rinsing process.
Microlithography processes for making miniaturized electronic components, such as in the fabrication of computer chips and integrated circuits, involve using photoresists. Generally, a coating or film of a photoresist is applied to a substrate material, such as a silicon wafer used for making integrated circuits. The substrate may contain any number of layers or devices thereon.
The photoresist coated substrate is baked to evaporate any solvent in the photoresist composition and to fix the photoresist coating onto the substrate. The baked coated surface of the substrate is next subjected to selective radiation; that is, an image-wise exposure to radiation. This radiation exposure causes a chemical transformation in the exposed areas of the photoresist coated surface. Types of radiation commonly used in microlithographic processes include visible light, ultraviolet (UV) light and electron beam radiant energy. After selective exposure, the photoresist coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed or the unexposed areas of the photoresist (depending upon whether a positive photoresist or a negative photoresist is utilized) resulting in a patterned or developed photoresist. Many developer solutions contain water and a base, such as water and a hydroxide compound.
Treating a selectively exposed photoresist with a developer conventionally involves depositing the liquid developer solution over the photoresist clad substrate and spinning the substrate whereby the liquid developer solution and dissolved areas of the photoresist are removed from the substrate by centrifugal forces. A rinsing solution, typically water, is then deposited over the photoresist clad substrate and the substrate is spun again to remove the water and any debris solubilized by the water. Spinning the substrate is a convenient and inexpensive method of removing materials from substrate. However, electrostatic charges build up on the developed photoresist during the development and water rinse cycles. Negative charges are particularly encountered on developed photoresists. While the causes of this phenomenon are not completely understood, it is believed that static charges and/or residual base (from the developer) contribute to charge accumulation. Charge accumulation on developed photoresists can be as high as 300-400 volts, and it is typically negative.
Negative charge accumulation on a developed photoresist presents a number of problems. One notable problem is that width measurement of various resist features, such as linewidth and profiling, is rendered inaccurate. Especially when using a scanning electron microscope (SEM) or an atomic force microscope (AFM), it is difficult to obtain accurate data. This is because SEMs and AFMs use an electron beam for generating images (both in projection and detection). The electron beam from the SEM or AFM is repulsed by the negative charge accumulated on the photoresist. The degree of repulsion or deviation from an ideal direction is dependent upon the magnitude of the accumulated negative charge.
This phenomenon is shown in FIG. 1. SEM 10 emits an electron beam (represented by the arrow(s)) towards a developed photoresist structure 12 on semiconductor substrate 14. The developed photoresist structure 12 has an accumulation of negative charge 16 as a result of the lithography process. Due to repulsion between the electron beam and the negative charge 16 of the developed photoresist structure 12, the electron beam path is altered away from the developed photoresist structure 12 without having deflected off or contacting the developed photoresist structure 12. Since the electron beam is not incident on the developed photoresist structure 12, an accurate measure/profile of the structure cannot be obtained. Detection of the altered electron beams provides data indicating at least one of inaccurate linewidth, fuzzy corner definition, and otherwise non-focused images. Assessment of the quality and parameters of a lithography process is consequently difficult or inaccurate and often impossible.
The present invention provides an improved rinsing process for photolithography. The present invention also provides systems and methods for minimizing charge accumulation on photoresist pattern covered substrates. As a result of the present invention, evaluation of a patterned photoresist, such as linewidth measurement, profile data, corner sharpness, critical dimension determinations, and image inspection, is substantially improved. Subsequent processing of semiconductor substrates after photolithography is accordingly improved.
In one embodiment, the present invention relates to a method of processing a photoresist on a semiconductor structure, involving the steps of exposing and developing the photoresist; evaluating the exposed and developed photoresist to determine if negative charges exist thereon; contacting the exposed and developed photoresist with a positive ion carrier thereby reducing any negative charges thereon; and evaluating the exposed and developed photoresist with an electron beam.
In another embodiment, the present invention relates to a method of reducing electrostatic charges on a developed photoresist to improve evaluation of the photoresist, involving the steps of contacting the developed photoresist with a positive ion carrier thereby reducing the electrostatic charges thereon by at least about 50%, wherein the positive ion carrier comprises an ionized gas, an acid solution, an onium solution, or a positive charge containing film; and evaluating the developed photoresist with one of a scanning electron microscope and an atomic force microscope.
In yet another embodiment, the present invention relates to a method of improving evaluation of a developed photoresist, involving the steps of contacting the developed photoresist with a positive ion carrier thereby reducing any negative charges thereon by at least 75%, the positive ion carrier comprising an ionized gas, an acid solution, a cation containing solution, or a positive charge containing film; and evaluating the developed photoresist with an electron beam, wherein the electron beam is generated from a scanning electron microscope or an atomic force microscope.
In still yet another embodiment, the present invention relates to a system for processing a patterned photoresist on a semiconductor structure, containing a charge sensor for determining if charges exist on the patterned photoresist and measuring the charges; a means for contacting the patterned photoresist with a positive ion carrier to reduce the charges thereon; a controller for setting at least one of time of contact between the patterned photoresist and the positive ion carrier, temperature of the positive ion carrier, concentration of positive ions in the positive ion carrier, and pressure under which contact between the patterned photoresist and the positive ion carrier occurs; and a device for evaluating the patterned photoresist with an electron beam.
In still another embodiment, the present invention relates to a system for reducing electrostatic charges on a developed photoresist to improve evaluation of the photoresist, containing an electrostatic charge sensor for determining if charges exist on the developed photoresist and measuring the charges; a means for contacting the developed photoresist with a positive ion carrier to reduce the charges thereon; a microprocessor-controller, coupled to the electrostatic charge sensor and the means for contacting the developed photoresist with a positive ion carrier, for setting at least one of time of contact between the developed photoresist and the positive ion carrier and concentration of positive ions in the positive ion carrier; and a scanning electron microscope for evaluating the developed photoresist with an electron beam.